What are the periodic maintenance tasks (weekly, monthly, annual, every X miles) that anyone who relies on a bike for transportation (typically in urban/semi-urban environments) should be performing? Ideally stated in terms of miles travelled (where applicable).

Good list. I'd like to add that the interval for lubing the chain will depend on the environment it's used in. Monthly is a good starting point, but if you bike in the rain a lot, it will not be enough. If you ride in really bad weather (especially combined with salt on the streets), you may have to lube the chain every few days.
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sleskeFeb 9 '11 at 10:43

@Batman: Yes, and so is a complete tear down. I've used bikes for years without ever tearing them down completely. Also, on modern bikes most bearings are not serviceable anyway (unlike old bearings, where this made sense).
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sleskeDec 31 '13 at 21:40

Being a big guy (~400lbs), I do a lot of damage to my bikes, so I check things more often and most of the time there isn't a problem. It's just better to double check. So as a result, here is my paranoid check schedule:

When needed:

Brake fine adjust (at the lever to maintain feel).

Chain lube.

Chain cleaning (if it has been wet out, this can be more often than below).

Clean disc brakes with rubbing alcohol.

Daily:

Tire pressure by feel (squeeeeze, it's like a hug for your tires!).

Brake feel (give it a good hard stab on my way out of the driveway).

Every 3 rides:

Accurate tire pressure.

Weekly:

Headset adjustment.

It's a quick check, takes all of 30 seconds if it isn't out of adjustment.

Note that many (most?) modern bottom brackets are sealed units, which do not need to (and usually cannot) be serviced, so no adjusting, let alone disassembling and greasing.
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sleskeFeb 9 '11 at 10:44

The "feel" of a brake lever isn't necessarily a good indicator of how well the brakes are setup. You can get a nice hard feeling if you have too little mechanical advantage, for example.
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BatmanJan 7 '14 at 4:31

@Batman Feel of the lever is more a personal adjustment that is important to me for panic stops, as well as a way to check for catastrophic failure, such as leaving cantilever brakes "open" after patching a tire.
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Jack M.Jan 8 '14 at 14:52

You should always carry spare batteries, especially in the winter months. I go one step further and have a set of very cheap (~3 dollars) lights on hand (the kind which stretches over the handlebars and seatpost) which will get me home in most cases and are better than nothing. And I think everyone should have lights on their commuter - you will eventually need them, even if you typically commute during the day.
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BatmanJan 7 '14 at 4:25

Please, please also check the adjustment of your light! During the past years I noticed more people use (LED) lights (which is great!) but have them pointing several kilometres to high - blinding everyone heading in their direction! :C
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yoshiMar 20 at 17:24

This depends greatly on the type of bicycle: a Dutch type commuter bike requires very little maintenance. Simply checking tire pressure weekly/monthly and maybe lubricating the chain once a year will keep it in good conditions for years (with minimal repairs needed).

The reason is that very few sensitive parts are exposed to weather and outside conditions: completely covering chaincase, internal hub gear, hub dynamo, etc.

My feeling is that it does help a lot to store the bike inside or at least under a roof to better protect it from rusting.

I'd think for most commuters who ride rain or shine, the hubs will need to be repacked at least yearly, even on a dutch bike.
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BatmanJan 5 '14 at 21:00

@Batman: I do commute daily in any weather (including snow) since childhood, but I've never disassembled the hubs, nor did they break down (or have I heard this happen to people I know).
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elderingJan 6 '14 at 10:36